The present invention relates to suppression of fluid-borne noise in hydraulic fluid handling systems, such as automotive power steering, power brake, air conditioning and fuel distribution systems, and more particularly to interconnection of fluid noise attenuation tuning cables in fluid handling systems.
There are many applications in industry and commerce where it is desirable to suppress fluid-borne noise in hydraulic power systems and other fluid handling systems. As an example, it is desirable to attenuate or suppress fluid-borne noise generated by the pump or fluid valving in automotive power steering, power brake, fuel distribution and air conditioning systems. It is also desirable to suppress compressor noise in domestic and commercial air conditioning systems. Fluid-borne noise can also be a problem in various industrial hydraulic systems where the fluid pressure pulses generate an audible and objectionable noise, causing wear and fatigue of system components, and potentially exceeding OSHA requirements.
The inherent design of fluid pumps, whether driven my an internal combustion engine, an electric motor or fluid system valves, causes pressure fluctuations or pulses in the fluid line that generate fluid-borne noise. The pistons, gerotors, gears, vanes or other fluid displacement elements that pump the fluid cause pressure fluctuations, ripple or pulses within the fluid at a frequency that is dependent on pump speed. The geometry and inherent characteristics of the pump can also be sources of fluid pressure fluctuations and vibrations. During normal operation of an automotive power steering system, for example, hydraulic fluid pressure can repetitively vary and thereby generate a pressure-dependent waveform that can range substantially in magnitude or amplitude between upper and lower values, and can cause or induce system vibrations. The frequency of such fluid-borne vibration also can vary substantially with the speed of the driving component (e.g., an engine) and other factors.
It has been proposed to employ noise compression cavities in fluid handling systems for suppressing this fluid-borne noise. The cavity may be of elastic hose material, for example, for suppressing pressure fluctuations by elastic attenuation. One or more tuning cables may also positioned within the cavity, of lengths associated with selected harmonics of the fluid-borne-noise, for enhanced noise attenuation. These cables conventionally comprise a pair of metal wires, such as steel, tightly spirally wound to form an elongated hollow tube, which is cut to desired length associated with the noise harmonics. The cable is secured within the cavity, and the ends of the cables are secured to each other where two tuning cables are used, by a restrictor or dogbone. This restrictor has a central tubular section and an enlarged cylindrical shell at one or both ends of the center section. This shell is conventionally swaged or mechanically crimped over the end of the tuning cable to secure the cable to the restrictor. The tuning cable or cables reduce the pressure ripple that causes fluid-borne noise by allowing a small amount of fluid to leak between the spiral wrappings into the cavity chamber that surrounds the cables.
However, problems are encountered associated with securement of the restrictor to the end(s) of the cable(s). Specifically, the spirally wrapped wires that form the tuning cable impart an undulating contour to the outer surface of the cable. When a mechanical crimping or swaging force is applied to the restrictor shell at a level sufficient to deform the shell inwardly around the undulating surface of the cable end, this force can cause separation between the spirally wrapped cable wires, resulting in excessive fluid leakage at the cable end. It is a general object of the present invention to provide a method of securing the restrictor to the end of a tuning cable length that reduces this fluid leakage problem, but maintains sufficient tensile strength at the restrictor/cable joint. Another object of the present invention is to provide a noise attenuation tuning cable assembly constructed in accordance with such method.
In general, the foregoing and other objectives are obtained in accordance with the invention by magnetically deforming the restrictor shell over an end of the tuning cable. The restrictor is preferably of relatively soft metal construction, such as brass or aluminum. AA6061 and AA6063 aluminum are particularly preferred. The restrictor may be heat treated to soften the material sufficiently to permit magnetic deformation over the end of the tuning cable while allowing the material of the restrictor shell closely to follow the undulating contour of the outer surface of the tuning cable end. It has been found that fluid leakage is greatly reduced while maintaining desirable tensile strength at the magnetically formed restrictor/cable joint.
A method of making a fluid noise attenuation tuning cable assembly in accordance with one aspect of the present invention comprises the steps of providing a length of tuning cable having metal wires spirally wrapped to form a hollow tube, and a restrictor having a hollow interior and an enlarged cylindrical end shell. An end of the tuning cable is placed within the restrictor end shell, and the restrictor end shell is magnetically deformed radially inwardly around the end of the tuning cable. The tuning cable assembly may include a single tuning cable secured to one end of the restrictor, or tuning cables of differing lengths secured to associated opposite ends of the restrictor.
A fluid noise attenuation tuning cable assembly in accordance with another aspect of the invention thus includes at least one length of tuning cable having wires spirally wrapped to form a hollow tube, and a restrictor having a hollow end shell received over an end of the tuning cable. The restrictor shell is magnetically deformed radially inwardly to grip the end of the tuning cable length. A pair of tuning cables may be secured to respective ends of the restrictor, with the tuning cables being of differing lengths. In the preferred implementation of the invention, the tuning cable assembly is disposed within an elastic hose, and a band externally secures the hose to the restrictor.